1. Field of the Invention
The present invention relates to a light source apparatus for a laser scanning optical system in a copying machine, a laser printer or the like. In particular, the invention relates to a technique for enabling adjustment of a distance between a light source and a collimating lens with a low-cost structure.
2. Related Art
Conventionally, in a copying machine, a printer, and the like, a laser beam is provided for scanning and forming an image. FIG. 7 shows one example of a laser scanning optical system to be used in a conventional copying machine or the like. In the laser scanning optical system shown in this drawing, a laser beam 2, emitted from a light source 1 such as a laser diode, is transmitted through a collimating lens 3 so as to be formed into a parallel light beam and is formed into a linear spot by a cylindrical lens 4 so as to enter a rotatable polyhedral mirror 5. The laser beam 2 which is deflected by the rotatable polyhedral mirror 5 is transmitted through an fxc2x7xcex8 lens 6 and forms an image on a scanning surface 7.
In order to maintain an emitted luminous flux, the distance between the light source and the collimating lens should be determined precisely. For this reason, the light source and the collimating lens are joined by a holding member such as a holder so as to be positioned and held. However, in such a structure, there arises a problem in that the holding member for joining the light source and the collimating lens undergoes thermal expansion due to a change in ambient temperature such as due to heat generated from a motor for driving a rotatable polyhedral mirror to be arranged in the vicinity of the holding member, heat generated from an electric circuit inside an apparatus such as a printer or a copying machine into which the light source apparatus is incorporated, a change in external temperature due to heat generated from the light source, and the distance between the light source and the collimating lens changes, and thus, the emitted luminous flux cannot be maintained in parallel and a defocusing occurs at the scanning surface. Therefore, particularly in a high-magnification laser scanning optical system, it is desirable that, in order to prevent the defocusing, the holding member for the light source and the collimating lens be composed of a material having a small linear expansion coefficient and that the distance between them can be adjusted.
Japanese Patent Application Laid-Open No. 5-129729 (1993) discloses a light source apparatus in which a collimating lens is fixed to an inside of a cylindrical mirror body, the mirror body is inserted into a cylindrical holder, and a laser diode is attached to a base section of the holder. In this light source apparatus, the mirror body is moved to a direction of an axial line so that the distance between the laser diode and the collimating lens is adjusted and after the adjustment is ended, the mirror body is fixed to the holder. The holder is generally made of a material such as an iron type sintered alloy having a small linear expansion coefficient so that the defocusing in use is suppressed.
However, when the holder and the mirror body are made of a sintered alloy so as to have a cylindrical shape, there arises a problem in that the cost of materials and the processing cost increase, and the cost of production becomes high.
It is an object of the present invention to provide a light source apparatus which is capable of adjusting a distance between a light source and a collimating lens with a low-cost structure.
The present invention provides a light source apparatus of the present invention, including a light source and a collimating lens for adjusting a luminous flux from the light source. The light source being supported by a holder made of a steel plate, a supporting member made of a steel plate is supported by the holder so as to slide in a direction of an optical axis of the collimating lens, and the collimating lens is supported by the supporting member.
In the light source apparatus having the above structure, since the supporting member which slides in the direction of the optical axis with respect to the holder supports the collimating lens, the supporting member is slid in the direction of the optical axis so that a distance between the light source and the collimating lens can be adjusted. Moreover, since the holder and the supporting member are made of a low-cost steel plate having a small linear expansion coefficient, a defocusing due to a change of temperature can be suppressed, and the production cost can be reduced. Moreover, when a mirror body is supported directly by the holder, it is necessary for sliding the mirror body with it being kept in a parallel orientation to secure a certain length of the mirror body. As a result, it is necessary to prepare a mirror body which is long in comparison with the overall length of the collimating lens to be held in the direction of the optical axis. However, in the present invention, since the supporting member for supporting the collimating lens is slid with respect to the holder, even if the mirror body is shortened, no problems arise.
Means for sliding the supporting member in the direction of the optical axis can be composed of an adjustment tool having a cam, a cam shaft, and a rotation operating section. In this case, a slot which extends in a direction substantially intersecting perpendicularly to the optical axis and into which the cam is housed is provided on the supporting member, and a hole into which the cam shaft is fitted inside the slot is provided to the holder. In this structure, when the adjustment tool is rotated, the cam urges the inner peripheral wall of the slot so as to move the supporting member in the direction of the optical axis. Alternatively, a screw is supported by one of the holder or the supporting member rotatably, and an end portion of the screw is screwed into the other one, and the cam is provided to a portion which contacts with the other member at a head portion of the screw.
The collimating lens can be supported directly by the supporting member. However, the collimating lens is fixed to the cylindrical mirror body and the mirror body is supported to the supporting member so that the structure can be more stable. In this case, the structure is simplified by forming a rectangular notch on the supporting member and supporting the outer peripheral surface of the mirror body by both edge portions of the notch. It is desirable to tighten and support the mirror body and the collimating lens elastically to the supporting member, and this suppresses displacement of the mirror body and the like due to oscillation. For example, it is preferable that a plate spring be formed into a gate shape and that both its end portions be fixed to the supporting member by screws, and a center portion of the plate spring be deformed elastically so that the mirror body and the like is tightened to the supporting member.
The holder and the supporting member can be formed by sheet-metal working, and as a material therefor, a cold-rolled material (normal steel plate) or a processed steel plate which was subject to plating can be used. The holder is bent perpendicularly at the time of sheet-metal working and the bent portion is used as the supporting portion of the light source so that the structure can be simplified. Moreover, a structure in which the supporting member is guided with respect to the holder can be formed easily by the sheet-metal working. For example, a plurality of slots which extend to the direction of the optical axis can be formed in the supporting member, and pins which slidably contact with the slots may be provided to the holder. In this case, the pins may be pressed into holes formed in the holder, or the pins may be formed integrally with the holder by fine blanking. Alternatively, a concave section which extends in the direction of the optical axis is formed in one of the holder and the supporting member, and a convex section which slidably contacts with the concave section can be formed in the other one. Such working can also be carried out easily by fine blanking.
The supporting member can be constituted so as to be moved to a direction intersecting perpendicularly to the optical axis (lateral direction). In this case, a slot which extends in the direction of the optical axis and in which the cam is housed is provided to the holder, and a hole into which the cam shaft is fitted may be formed in a frame of a copying machine, for example, to which the light source apparatus of the present invention is attached.